802.1AB Overview Configuring 802.1AB
page 13-4 OmniSwitch AOS Release 7 Network Configuration Guide June 2013
802.1AB Overview
LLDP is a Layer 2 protocol used to detect adjacent devices in a network. Each device in a network sends
and receives LLDPDUs through all ports on which the protocol is enabled. If the protocol is disabled on a
port, then LLDPDUs received on that port are dropped.
The LLDPDUs are transmitted at a certain interval. This transmission interval can be configured. When an
LLDPDU is received from a neighboring device, the LLDPDU software validates the frame and stores the
information in the remote device Management Information Base (MIB). This information ages
periodically. If an LLDPDU is not received from the same device within the time specified in the TTL
TLV of the LLDPDU, the information is updated in the related MIB. By exchanging information with all
the neighbors, each device gets to know its neighbor on each port. The information contained in the
LLDPDU is transmitted in the TLV (Type, Length, Value) format and falls under two categories:
• Mandatory
• Optional
Each LLDPDU contains all the five mandatory TLVs and optional TLVs.
Mandatory TLVs
The mandatory TLV information contains the following information with regard to the LAN device:
• MSAP (MAC service access point) identifier.
• Time period for the validity of the information
The mandatory TLVs contained in an LLDPDU are listed below:
• Chassis ID TLV
• Port ID TLV
• VLAN ID TLV
• Time to live TLV
• End of LLDPDU TLV
Optional TLVs
The optional TLVs defined as part of LLDP are grouped into the following sets listed below:
Basic Management TLV Set
• Port Description TLV
• System Name TLV
• System Description TLV
• System capabilities TLV
• Management address TLV
Note. This optional TLV set is required for all LLDP implementation.
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